Abstract: In this paper, the design of an X-band dual-balanced mixer based on a novel broadband HMSIW balun is presented. The operation mechanism of the balun is based on the fact that the phase difference of waveguide surface current between the top and the bottom is 180 degrees. With the advantage of the HMSIW architecture, these mixers have the feature of good balance, wide bandwidth, compact size and low cost. In the frequency band from 8.7 -9.7GHz, the conversion loss of the mixer is less than 9dB, and minimum is 7.3dB. Noise figure is less than lOdB, and full size is 60ram ×68mm.